This invention relates generally to swath printing, and more particularly to inkjet printers using separate nozzle arrays for each different color ink.
While much research and development has been directed toward increasing the nozzle resolution on inkjet printheads as the best way to improve print quality, some benefits can also be obtained through print mode techniques. Higher resolution addressability has already been obtained to some degree with monochrome print mode techniques. Examples of this are found in U.S. Pat. No. 5,541,625 issued Jul. 30, 1996 for METHOD FOR INCREASED PRINT RESOLUTION IN THE CARRIAGE SCAN AXIS OF AN INKJET PRINTER; U.S. Pat. No. 5,469,198 issued Nov. 21, 1995 entitled MULTIPLE PASS PRINTING FOR ACHIEVING INCREASED PRINT RESOLUTION; and U.S. Pat. No. 5,535,307 issued Jul. 9, 1996 entitled PRINTING OF VARIABLE DOT SIZES DEPENDENT UPON IMAGE DENSITY FOR IMPROVED GRAPHICS.
The monochrome techniques for increased addressable resolution, and the related depletion techniques, are not easy to apply to color printing, particularly where the goal is to have increased resolution in both the X and Y axes (media advance and carriage scan axes, respectively) as generally labeled for wide format printers/plotters.
An increased color resolution printer from Epson was introduced which provided some color depletion after increasing addressable resolution to 720xc3x97720. This product was unfortunately based on a very low nozzle resolution printhead of 90 dpi, which required a slow tedious eight pass print mode as well as special media to decrease ink dot gain.
So there still remains a need for a faster increased resolution higher resolution print technique which includes improved dot depletion to assure better print quality for a wider selection of media.
The invention provides a swath printing system such as multi-color inkjet printing which uses lower resolution printheads of at least 300 dpi nozzle spacing to achieve high resolution output of at least 600 dpi addressability in both the X (media advance) and Y (carriage scan) axes.
Increased resolution is achieved in the X axis in a first embodiment by printing on a first carriage pass a first set of color ink drops onto a first group of pixel rows spaced apart at the lower resolution distance (e.g., 1/300 inch) and extending longitudinally in the Y axis direction, advancing the media to re-position the nozzles, and then printing on a second carriage pass a second set of ink drops onto a second group of different pixel rows also spaced apart at the lower resolution distance and extending longitudinally in the Y axis direction, with the second group of pixel rows interlaced between the first group of pixel rows. A related feature of the invention is to advance the media in a preferred four pass print mode, with even and odd numbered pixel rows being printed on alternate swaths based on advancing the media different distances between each swath.
A second embodiment provides increased resolution in the X axis by the offset positioning of two printheads of the same color ink with their respective nozzles mis-aligned in the Y axis direction so that both the aforesaid first and second group of interlaced pixel rows can be printed on the same carriage pass, the first group by nozzles of one printhead and the second group by nozzles of the other.
Increased resolution is provided in the Y axis in a first embodiment having a single printhead for each color by any of the following:
1) maintaining the same carriage speed and the same firing frequency for the printhead, and printing on a first carriage pass a first set of color drops onto a first group of pixel columns spaced apart at the lower resolution distance (e.g., 1/300 inch) and extending in the X axis direction, and then printing on a second carriage pass a second set of ink drops onto a second group of different pixel columns also spaced apart at the lower resolution distance and extending in the X axis direction, with the second group of pixel columns interlaced between the first group of pixel columns;
2) maintaining the same carriage speed but doubling the firing frequency for the printhead, so that both the aforesaid first and second group of interlaced pixel columns can be printed on the same carriage pass; or
3) moving the carriage at half the usual speed, but maintaining the same firing frequency for the printhead, so that both the aforesaid first and second group of interlaced pixel columns can be printed on the same carriage pass.
Increased resolution is provided in the Y axis in a second embodiment by having two printheads for each color offset in the X axis direction so that both the aforesaid first and second group of interlaced pixel rows can be printed on the same carriage swath.
A further feature of the invention is the use of a plot-independent depletion mask for area fills which improves print quality.
Synchronized depletion masks for area fills and edge enhancement are provided which are plot independent and prevent drop overlap. It is especially suited for multi-pass print modes since each row has a balanced number of pixels, and there are no rows which have no xe2x80x9conxe2x80x9d pixels. The depletion includes separate depletion masks and rules for edge enhancement as compared to area fills. Each color plane is depleted separately, but subject to the same depletion rules and masks. A separate depletion step provides for narrowing the vertical and horizontal dimensions of the figure to be printed.